Differential system and method for operation of a differential system

ABSTRACT

Methods and systems for a locking differential are provided. The locking differential system includes an electromagnetic solenoid actuator designed to induce locking and unlocking of the differential and a circuit board assembly designed to programmatically control the locking and unlocking functionality. The circuit board assembly includes a sensor and control circuity enclosed in a continuous sealed enclosure, the sensor extends down the face of a coil assembly in the solenoid.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a divisional of U.S. Non-Provisional patentapplication Ser. No. 17/024,561, entitled “DIFFERENTIAL SYSTEM ANDMETHOD FOR OPERATION OF A DIFFERENTIAL SYSTEM”, and filed on Sep. 17,2020. The entire contents of the above-listed application are herebyincorporated by reference for all purposes.

TECHNICAL FIELD

The present disclosure generally relates to a locking differentialassembly in a vehicle. More particularly, the present disclosure relatesto a solenoid actuator as well as control and sensing circuitry of theactuator.

BACKGROUND AND SUMMARY

Some drivetrains include differentials with locking capabilities whichwhen activated, prevent speed differentiation between drive wheels. Incertain locking differentials, electronic actuators are used, owing inpart to their quicker actuation times and increased durability incomparison to certain pneumatic locking systems and other types oflocking mechanisms.

US 2019/0195327 A1 to Creech et al. teaches an electronic differentiallocker with a sensor adjacent to a locking armature. The inventors haverecognized several drawbacks with US 2019/0195327 A1 and otherelectronic locking mechanisms. Although, US 2019/0195327 A1 generallyteaches a controller and a sensor coupled to the electronic actuator,the controller's programmatic capabilities are limited to electricallyenergizing the actuator in the differential assembly. Moreover, thecontroller is spaced away from the sensor and exhibits a bulky profilewhich may pose packaging challenges in space constrained differentials.

Furthermore, the components in the electrical differential lockerdisclosed in US 2019/0195327 A1 are located in a relatively harshinterior environment of the differential. For instance, these componentsmay experience elevated levels of heat and vibration and may be exposedto oil. These environment conditions may increase the likelihood ofcomponent degradation, in comparison to electronics spaced away from thedifferential. Other electronically actuated differential systems haverelied on remotely located controllers to implement more complex controlstrategies. However, when vehicles deploy this type of system, design ofthe locking mechanism's control logic (e.g., population and calibrationof circuitry) at a separate stage from the manufacture and assembly ofthe differential may be demanded. The precision of current control tothe locking mechanism be decreased due to the uncoordinated differentialand control logic manufacturing steps.

To overcome at least some of the aforementioned challenges, adifferential system is provided. The differential system, in oneexample, comprises an electromagnetic solenoid actuator that includes acoil assembly and a piston. The piston is configured to selectivelyinduce locking and unlocking of axle shaft speed differentiation in thedifferential. The system further comprises a circuit board assemblyconfigured to programmatically control the electromagnetic solenoidactuator. The circuit board assembly includes control circuitry and asensor that is configured to sense a position of the piston and radiallyextends down a face of the coil assembly. Further, in the system, thesensor and the control circuitry are enclosed in a sealed housing. Inthis way, a sensor and control circuitry are compactly incorporated intoa locking differential and achieve desired thermodynamic characteristicswhich reduce the likelihood of the electronic components experiencingover-temperature conditions. The system's applicability and customerappeal may be increased as a result of the reliable and space efficientcontrol and sensor circuitry arrangement.

In another example, the circuit board assembly may further includeexecutable instructions stored in non-transitory memory that cause thecircuit board assembly to periodically place the circuit board assemblyin a lower power consuming state for a selected duration. In this way,the control circuitry may be put to sleep for a desired duration todecrease the circuit's power consumption and temperature,correspondingly. Accordingly, the chance of the circuit experiencingover-temperature conditions may be further reduced and customer appealmay be correspondingly increased. Further, in one example, the durationof circuit's sleep state may be less than the time scale of the lockingmechanism operation. In this way, the differential retains lockingfunctionality while the control circuitry is put to sleep periodically.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows an illustration of an embodiment of a differential systemwith a circuit board assembly.

FIG. 2 shows an exploded view of the differential system and circuitboard assembly, depicted in FIG. 1 .

FIG. 3 shows a detailed view of the circuit board, depicted in FIG. 2 .

FIG. 4 shows a cross-sectional view of a use-case differentialincorporating the circuit board assembly, depicted in FIGS. 1-3 .

FIG. 5 shows a method for operation of a differential system.

FIG. 6 shows a timing diagram of a use-case control strategy for adifferential system.

DETAILED DESCRIPTION

FIGS. 1-3 are drawn approximately to scale. However, other relativecomponent dimensions may be used, in other embodiments.

A differential system with an electronic locking mechanism and controlstrategy for the locking mechanism is described herein. The differentialsystem includes a circuit assembly with a control board and an actuatorsensor. The control board and sensor form a common structure that iscoupled to the locking mechanism's electronic actuator. Packaging thesensor and control circuitry in a common structure within thedifferential enclosure allows downstream vehicle manufacturers to forgopopulating and calibrating the electronic locker's control circuitry, ifdesired. The differential system's market appeal is consequentlyincreased. Incorporating the control circuitry and sensor into thelocking mechanism's electronic actuator may allow the precision ofactuator control to be increased, if wanted. To elaborate, in certainmanufacturing scenarios, the control strategy for the solenoid actuatormay unfold with greater precision due to cooperative manufacture of thecontrol circuitry and the solenoid actuator. The coordinated manufactureof the control circuit and the solenoid actuator may allow the actuatorto be calibrated to achieve even greater control precision, whichfurther increases the solenoid's performance.

In the system, the control circuitry and internal logic are designed toenable the electronics to withstand the relatively high temperaturesexperienced inside the differential, efficiently dissipate heatgenerated by the control circuitry, and cooperatively seal the controlcircuitry and an actuator sensor. In this way, the locking mechanism'scircuitry may be deployed in axle enclosures that may impose spaceconstraints and relatively small thermal margins for circuit operation(around 5° C., in certain use-cases). In one example, the sensor mayextend in a plane parallel to a face of the actuator and form an L-shapewith a control circuit board to achieve targeted thermodynamic, sensing,and sealing characteristics. Consequently, the system's reliability maybe increased due to a reduction in the chance of the circuitryexperiencing over-temperature conditions or degradation caused bylubricant interfering with the circuitry. To elaborate, the controlcircuit board may confidently implement locking control and diagnosticstrategies, even when deployed in an environment with comparatively highexpected operating temperatures. Further, in one example, the controlcircuitry may be periodically put to sleep (e.g., a lower or near zeropower consuming state) for a selected duration which reduces thetemperature of the circuitry. In this way, the circuit may be designedto cope with the higher temperature conditions inside somedifferentials. The circuitry's sleep duration may be selected to reducethe circuit's power consumption while the differential's lockingfunctionality remains operational. For instance, the sleep duration maybe less than the time scale of the locking mechanism's energizationcontrol. In this way, the locking mechanism's control circuitry may beput to sleep to reduce the heat generated by the circuit and allow thecircuitry to remain with targeted thermal margins. The circuitry maytherefore be deployed in a wide variety of differentials, such asdifferentials which may reach high temperatures (e.g., around 150° C. incertain scenarios) during operation.

FIGS. 1-2 show a differential system with a circuit board assembly for alocking mechanism which is thermodynamically designed to function inhigher temperature environments. FIG. 3 shows a detailed view of thecircuit board assembly which is shaped to facilitate solenoid actuatorsensing and space the control circuit away from the solenoid's heatgenerating coils. FIG. 4 shows a cross-sectional depiction of adifferential embodiment that employs the circuit board assembly withcontrol, sensing, and diagnostic circuitry for the locking mechanism'ssolenoid actuator. FIG. 5 shows a method for operating a differentialsystem and triggering differential locking as well as operating thecircuitry in a lower power consuming state. FIG. 6 shows a timingdiagram for a use-case differential system control strategy whichperiodically places the control circuitry in a lower power state whilelocking operation unfolds to reduce circuitry heat generation.

FIG. 1 shows a differential system 100 (e.g., locking differentialsystem). The differential system 100 may be included in a vehicleschematically depicted at 101. The vehicle 101 may be a light, medium,or heavy duty vehicle. Said vehicle, in one example, may be a vehicleutilizing an internal combustion engine as a motive power source. Inanother example, said vehicle may be an electric vehicle, such as abattery electric vehicle (BEV) or a hybrid electric vehicle. In thehybrid vehicle example, both the motor system and an internal combustionengine may be used to generate motive power, while in the BEV examplethe internal combustion engine may be omitted. A BEV may have a lesscomplex powertrain configuration which may drive down the chance ofpowertrain degradation, in certain cases.

The differential system 100 includes an electromagnetic solenoidactuator 102 designed to induce locking and unlocking of a differentiallocking mechanism schematically depicted at 104. Arrows 105 indicate thelocking and unlocking action between the actuator and the lockingmechanism. The differential locking mechanism may include componentssuch as a locking plate designed to engage and disengage speeddifferentiation between the differential's side gears. Although thedifferential locking mechanism is schematically illustrated, it will beunderstood that the locking mechanism has greater structural complexity,which is expanded upon herein with regard to the FIG. 4 . As describedherein, when the differential is locked, speed differentiation betweenaxle shafts is substantially inhibited and when the differential isunlocked, speed differentiation between the axle shafts is permitted.

A circuit board assembly 106 is further provided in the differentialsystem 100. The circuit board assembly 106 includes control circuitry108 and a sensor 110. In one example, the control circuitry 108 may bepositioned on an upper side 111 of the solenoid actuator 102.Positioning the control circuit on the upper side of the actuatorenables the circuit to be spaced away from a lubricant sump. The sensor110 is designed to sense the position of a piston 112 in the solenoidactuator 102. Specifically, in one example, the sensor 110 may be aneddy current sensor. However, other suitable sensors have beenenvisioned. Thus, the sensor 110 may send signals indicative of thepiston's position to the control circuitry in the circuit boardassembly. The sensor 110 may extend down a first face 114 of thesolenoid actuator 102. In this way, the sensor 110 may be arranged in adesired orientation to achieve targeted solenoid sensing functionality.To elaborate, the sensor 110 may be arranged parallel to the plane ofthe solenoid actuator face 114.

The circuit board assembly 106 may be in electronic communication with avehicle controller 116 (e.g., electronic control unit (ECU)) via wiredand/or wireless communication. The vehicle controller 116 may thereforebe spaced away from the circuit board assembly. The vehicle controllermay be designed to implement control strategies such as engine control,motor control, powertrain control, and the like. The circuit boardassembly 106 may send rapidly distinguishable messages, such as messagesindicating the circuit board assemblies state (e.g., activated higherpower consuming state or a lower power consuming state (sleep state)),to the vehicle controller. To accomplish the aforementioned vehiclecontrol functionality, the vehicle controller may include a memory 118storing instructions executable by a processor 120 to carry out thevehicle control strategies.

An axis system 150 is provided in FIG. 1 as well as FIGS. 2-4 , forreference. The z-axis may be a vertical axis (e.g., parallel to agravitational axis), the x-axis may be a lateral axis (e.g., horizontalaxis), and/or the y-axis may be a longitudinal axis, in one example.However, the axes may have other orientations, in other examples. Acentral axis 152 of the differential system 100 is further provided inFIG. 1 and FIGS. 2 and 4 , for reference. It will be understood that thecentral axis 152 may be the rotational axis of the axle shafts in thedifferential system. As described herein, axial movement may refer to acomponent's movement along a direction parallel to the central axis.

FIG. 2 shows an exploded view of the differential system 100. Theelectromagnetic solenoid actuator 102 and the circuit board assembly 106are again depicted. As indicated above, the solenoid actuator 102 isdesigned to trigger differential locking and unlocking. To accomplishthe locking-unlocking functionality, the electromagnetic solenoidactuator 102 includes a coil assembly 200 and the piston 112. The coilassembly 200 is electrically coupled to an energy source 202 (e.g.,battery, capacitor, alternator, etc.). The coil assembly 200 may beenergized to induce axial movement of the piston 112 to trigger lockingand unlocking of the differential. The piston 112 may therefore functionas an armature, in one example. In particular, the coil assembly 200 maybe selectively energized and de-energized to induce activation anddeactivation of the electromagnetic solenoid actuator 102. Activationand deactivation of the solenoid actuator causes differential lockingand unlocking.

In one example, the electromagnetic solenoid actuator 102 may beactivated via a multi-stage control strategy. Therefore, in someinstances, the solenoid actuator may, in a first stage, be energizedwith a higher current to induce movement of the piston 112 and in asecond stage, be energized via a lower current to hold the piston in adesired position. Thus, in one specific embodiment, the solenoidactuator may be activated via a peak and hold strategy where the currentdelivered to the solenoid is stepped down during activation. When thecircuit board assembly 106 is incorporated into the differential andmanufactured therewith, the precision in solenoid actuator control maybe increased, thereby increasing actuator performance and vehiclehandling performance, correspondingly. Incorporating the circuit boardassembly 106 into the differential further enables the circuit boardassembly 106 to be more precisely calibrated when manufactured, incertain cases. For instance, a sole manufacturer may assemble thedifferential and control circuitry and then subsequently calibrate thecontrol circuitry. Consequently, the precision in solenoid actuatorcontrol may be further increased, which increases actuator performance.

The electromagnetic solenoid actuator 102 may further include a washer204. The washer 204 may function to axially retain components in theactuator. The solenoid actuator 102 may further include a housingassembly 206. The housing assembly 206 may include a housing 208 and aplate 210. When assembled, the electromagnetic solenoid actuator 102 isfluidly sealed within the housing 208 and the plate 210. In this way,the solenoid may be protected from lubricating fluid (e.g., oil) withinthe differential enclosure. The plate 210, in one example, includes arecess 211 profiled to mate with the sensor extension 213 of a circuitboard assembly housing 226, expanded upon herein. In this way, thecircuit board assembly may be sealed with the solenoid actuator 102. Therecess 211 may have a shape which correlates to the shape of the sensor110. As such, in one example, the recess may have two opposing walls 227which are parallel to one another and profiled to seal the sensor.However, other recess shapes have been contemplated.

The coil assembly 200 may include the first face 114 (e.g., inner axialface), a second face 212 (e.g., outer axial face) opposite the firstface, and an outer circumferential surface 214 extending between thefirst and second faces. These solenoid components may enclose coilwindings which when energized cause the piston 112 to move in an axialdirection.

The control circuit 108 is designed to implement control and diagnosticstrategies. For instance, the control circuit 108 may selectivelyenergize the solenoid actuator to induce locking and unlocking of thedifferential based on one or more operating conditions. Various controland diagnostic strategies programmatically stored in the control circuit108 are discussed in greater detail herein with regard to FIGS. 5-6 . Toaccomplish the control and diagnostic functionality the control circuit108 may include memory executable by a processor. The memory may storeinstructions executable by the processor to carry out the controlmethods, strategies, etc. described herein. To elaborate, the processormay include a microprocessor unit and/or other types of circuits. Thememory may include known data storage mediums such as random accessmemory, read only memory, keep alive memory, combinations thereof, etc.The circuit board assembly 106 may be included in a control system 216which further includes one or more input devices such a button,graphical user interface (GUI), knob, switch, slider, and the like whichenable a system operator to initiate differential locking and unlockingfunctionality. Additionally or alternatively, the circuit board assembly106 may be designed to programmatically lock and unlock the differentialbased on operating conditions such as vehicle speed, vehicle traction,vehicle load, and the like.

The housing 208 may include a cut-out 218 which extends through acircumferential surface 220 and an outer wall 222. The cut-out 218 matesand seals the circuit board assembly 106. In this way, circuit boardassembly 106 may be space efficiently incorporated into the solenoidactuator while fluidly sealing the actuator from lubrication fluidpresent in the differential. The cut-out 218 may specifically includeopposing walls 224. The profile of the walls 224 may correspond to theprofile of the circuit board assembly housing 226. Specifically, in oneexample, the walls 224 may be parallel to one another to enable thecircuit board assembly to be efficiently sealed with the solenoidactuator. However, other wall profiles have been envisioned. Theactuator housing 208 may further include an inner circumferentialextension 228 (e.g., annular extension) designed to mate with a sectionof the differential such as a differential case.

The control circuit 108 and the sensor 110 may form an L-shape, in oneexample. To elaborate, the sensor 110 may be arranged at a substantiallyperpendicular angle 230 to the control circuit 108. Thus, as shown thecircuit board assembly 106 may include a continuous base 232 thatcomprises an upper section 234 and a side section 236 that radiallyextends towards the central axis 152. In this way, the sensor 110 may bearranged at a desired angle for sensing operation while allowing thecontrol circuit to be spaced away from the solenoid coils which generateheat during operation.

The circuit board assembly 106 further includes the sealed housing 226with a first section 238 which may have an L-shape profile correspondingto the L-shape of the underlying circuit board. The L-shaped housingallows the assembly to achieve a comparatively small package, sensesolenoid actuator movement, and exhibit targeted thermal characteristicswhich reduces the heat of the circuit. A second section 240 (e.g.,cover) may, when assembled, attach to the first section 238 to seal thecircuit board therein. The second section 240 may include a planar facewhich increases heat transfer from the circuit to the surroundingenvironment while the housing achieves a space efficient profile. Thesecond section 240 may mate in an opening 241 of the first section 238.The second section 240 further includes a planar top surface 243 whichmay be laterally aligned which allows the housing to transfer greateramounts of heat to the surrounding environment.

The housing 226 may include a wiring interface 242 (e.g., wiringharness). In one embodiment, the wiring interface 242 may be acontroller area network (CAN) wiring interface with four wire ports 244,as illustrated. However, in other embodiments, the wiring interface 242may be a local interconnect network (LIN) wiring interface with threewire ports (one signal wire, one power wire, and one ground wire). Whena CAN wiring interface is deployed, degradation of the circuit board'scomponents may be more easily identified. On other hand, when an LINwiring interface is deployed, the likelihood of wire degradation isdecreased, due to a reduction in wires and packaging of the circuitboard assembly may be simplified, in certain scenarios. The wire ports244 may be arranged along an axis 246, shown in FIG. 3 , parallel to thecentral axis 152. In this way, the circuit board assembly 106 mayachieve a space efficient form which spaces the heat producing sectionsof the board away from the coil assembly 200 which generates heat duringoperation. Consequently, the chance of the circuit board assembly'stemperature surpassing a desired value may be reduced.

The circuit board assembly 106 may further include wire seals 248coupled to the wiring interface 242 to reduce the chance of lubricantinterfering with the wiring and entering the circuit board enclosure. Inthis way, the assembly's longevity may be further increased.

FIG. 3 shows a detailed depiction of the control circuit 108 and thesensor 110 in the circuit board assembly 106. As depicted, thecontinuous base 232 may be provided in the circuit board assembly. Thecontinuous base 232 may include the upper section 234 with the controlcircuitry and the side section 236. Similar to the assembly's housing,the upper section 234 may be arranged at a substantially perpendicularangle 230 to the side section 236. This L-shaped board, allows the boardto achieve desired sensing, sealing, and thermal characteristics, whichincrease the circuit board's longevity. The upper section 234 includescircuitry which may include memory and a processor designed to implementthe control strategies, methods, and/or diagnostics described herein.The side section 236 includes circuitry such as eddy current sensorcircuitry configured to sense movement of the solenoid piston. Theboard's wiring interface 242 is again shown with the wire seals 248 onthe wire ports.

FIG. 4 shows a use-case example of a differential system 400. Thedifferential system 400 includes an electromagnetic solenoid actuator402 and a circuit board assembly 404 which may share at least some ofthe structural and functional features with the electromagnetic solenoidactuator 102 and the circuit board assembly 106, shown in FIGS. 1-3 .

The differential system 400 may include a gear 406 (e.g., ring gear)which may be coupled to a drivetrain gear (e.g., pinion gear). The gear406 may be rotationally coupled to a prime mover (e.g., internalcombustion engine, motor, combinations thereof, and the like)schematically depicted at 408. Arrows 410 indicate the flow of powerbetween the prime mover and the gear 406.

The gear 406 is coupled to a shaft 412 on which gears 414 (e.g., piniongears) reside. The gears 414 are coupled to side gears 416, 418. Inturn, the side gears 416, 418 are coupled to axle shafts 420, 422 (apair of axle shafts) which may be rotationally coupled to drive wheels424 indicated via arrows 425. Splines 426 and/or other suitableattachment interfaces may facilitate attachment between the axle shaftsand the side gears 416, 418. The differential system 400 may furtherinclude a case 428 coupled to the gear 406.

A locking gear 430 in a locking device 432 of the differential system400 may be actuated via the solenoid actuator 402. Thus, the lockinggear 430 may be placed in an unlocked position and a locked position viathe actuator. In the unlocked position, teeth 434 in the locking gear430 are spaced away from teeth 436 in the side gear 416, in one example.Continuing with such an example, conversely, in the locked position, theteeth 434 in the locking gear 430 are mated with the teeth 436 in theside gear 416. In this way, the differential may be locked and unlockedvia the locking device 432. However, other suitable types of lockingmechanisms have been contemplated. The differential system may furthercomprise springs 431 arranged between the locking gear 430 and the sidegear 416. The springs function to return the locking gear to an unlockedposition. However, other locking device configurations have beencontemplated.

The solenoid actuator 402 may be coupled to a body section 438. Thecircuit board assembly 404 again arranges a sensor 440 down a face 442of the solenoid actuator 402. Control circuitry 444 may again laterallyextend across a top side 446 of the solenoid actuator 402. In this way,the circuit board assembly 404 may be spaced away from lubricant 448(e.g., oil) which is stored in a lubricant reservoir 450 (e.g., sump) ofan axle housing. Consequently, the likelihood of the lubricantinterfering with circuit operation is reduced. A housing 452 of thesolenoid actuator 402 is further depicted in FIG. 4 . The housing 452 atleast partially encloses a coil assembly 454 in the solenoid actuator.Specifically, the housing 452 seals the coil assembly 454 and thecircuit board assembly 404 to the solenoid actuator.

FIG. 5 shows a method 500 for operation of a differential system. Themethod 500 may be implemented by one or more of the differential systemsand corresponding components, described above with regard to FIGS. 1-4 .Therefore, the method 500 may be carried out via a circuit boardassembly incorporated in a differential system. Further, the circuitboard assembly may include a controller including memory holdinginstructions executable via a processor, as previously discussed.

At 502, the method includes determining operating conditions. Theoperating conditions may include ambient temperature, circuit boardassembly temperature, electromagnetic solenoid actuator temperature,vehicle speed, vehicle load, operator input device configuration, etc.The operating conditions may be determined via sensing and/or modelingtechniques.

At 504, the method includes determining whether or not to implementdifferential locking. Various factors may be taken into account whendetermining if differential locking is desired. For instance,differential locking may be initiated when a vehicle operator actuates abutton, or other input device, indicating the operator's desire to lockthe differential. In other examples, the differential may be locked whenthere is a vehicle traction imbalance between the drive wheelsrotationally coupled to the differential. For instance, if drive wheelspeed deviation surpasses a threshold value (e.g., 0.8 meters per second(m/s), 1.4 m/s, 2.2 m/s, etc.) differential locking may be initiated.

If it is determined that differential locking is not desired (NO at504), the method moves to 506 where the method includes sustaining thedifferential locking mechanism in the unlocked or locked configuration.

If it is determined that differential locking is desired (YES at 504),the method advances to 508. At 508, the method includes energizing thesolenoid actuator to trigger differential locking. For example,energization of the solenoid actuator may move the actuator's pistonsuch that it urges a locking plate into engagement with a side gearwhich substantially prevents speed differentiation between thedifferential's side gears. As previously discussed, the energization mayunfold in two stages, with the first stage having a greater current flowto the solenoid than the second stage.

At 510, the method includes periodically placing the control circuitryin the circuit board assembly in a lower power consuming state. A lowerpower consuming state may be a sleep state where the circuit consumesless power than in the activated state of the circuit. For instance,when the circuitry is put in the lower power consuming state (e.g.,sleep state), the circuitry state may be held in memory (e.g., randomaccess memory) and the other subsystems in the circuit and the memorymay be placed in a low power state (e.g., minimum power state) whichallows the memory to retain data. Thus in one example, the controlcircuitry may be put to sleep for a first duration and the activatedstate for a second duration. The first duration may be greater than thesecond duration, in one example. For instance, the first duration may be70 milliseconds (ms) and the second duration may be 30 ms, in oneuse-case example. However, numerous suitable sleep durations have beenenvisioned. To allow differential locking and unlocking to unfold whileputting the circuit cyclically to sleep, the time scale of the lockingfunctionality may be greater than the duration of the lower powerconsuming state (e.g., sleep state). For instance, the lockingdifferential control strategy may be operated on a time scale of onesecond or half of a second. In such an example, the sleep duration maybe less than half a second. Further, in one example, the duration of thelower power consuming state may be adjusted based on operatingconditions such as control circuitry temperature, ambient temperature,vehicle speed, vehicle load, combinations thereof, etc.

At 512, the method may include periodically implement sensing and/orcontrol circuit diagnostics. For instance, degradation of the controlcircuit and/or sensing circuit may be ascertained via the diagnosticroutines. Diagnostic routines for the internal circuitry, lockingactuator position, solenoid actuator, and/or control circuitry interfacemay be implemented. Generally, a diagnostic routine may includeascertaining operating conditions based on sensor signals and/orcondition modeling. The diagnostic routine may subsequently make adetermination if one or more of operating conditions is not within adesired range, exceeds or falls below a threshold value, etc. andtrigger a flag if the targeted operating condition(s) are not fulfilled.For instance, various aspects of the control circuitry (e.g.,microcontroller) may be diagnosed such as the memory's validity, aprogram bug (e.g., undesirable programmatic operation), a program error(e.g., detected by a watch dog timer designed to generate a time-outsignal based on an error), and/or an over-temperature condition of thecircuit. Thus, in one example, an over-temperature diagnostic flag maybe set when the circuit exceeds a threshold value. Aspects of the sensorsuch as the position sensor signal's range and/or the drive current'srange exceeding targeted values may further be diagnosed. Features ofthe circuit's power drive may be diagnosed such as the power drivesignal level and shorts in the output drive such as shorts to ground orshorts to the battery. For instance, one diagnostic routine may verifyif a signal level capable of operating the power drive is present.Diagnostic techniques may further include diagnostics related to thelocking actuator position, such as a strategy which decides if theactuator's sensed position is out of range. Other diagnostic techniquesmay include actuator diagnostics ascertaining if the actuator coil isopen or if the actuator coil has shorted. The circuit's communicationinterface may further be diagnosed. As such in one exemplary diagnosticmethod, the logic may determine if a communication link has been lost orif the communication data is invalid.

At 514, the method may include sending and/or receiving messages from avehicle controller. For instance, the circuit board assembly may sendthe vehicle ECU messages which indicate that the circuit board assemblyhas powered up, powered down, and/or is operational (e.g., passed adiagnostic test). Thus, the messages may be circuit board state updatesthat indicate the state of the circuit board assembly. In this way, thecircuit board assembly may efficiently communicate with the vehicle ECUto increase data available to the ECU without unduly increasingprocessing resources used to gather and interpret the data from thedifferential's control circuitry. Method 500 allows the circuit boardassembly to be operated with relatively small thermal margins, ifdesired, due to the reduction in heat generated by the circuitry. Method500 further allows the solenoid actuator's control circuit toefficiently communicate with the vehicle ECU, if wanted, to decrease thecomputing resources the ECU devotes to the management of data from thedifferential system.

FIG. 6 illustrates a timing diagram 600 of a use-case control strategyfor a differential system, such as the differential systems shown inFIGS. 1-4 . However, the control strategy may be implemented viaalternate suitable differential systems. In each graph of the timingdiagram, time is indicated on the abscissa. The ordinate for plot 602indicates the states (“Locked” and “Unlocked”) of the differential'slocking device. The ordinate for plot 604 indicates the states(“Activated” and “Sleep”) of the control circuit.

At t1, the locking mechanism transitions from an unlocked state to alocked state. Further, as shown in plot 604, the control circuit isperiodically placed in a sleep state which consumes less power than inthe activated state. Thus, the control circuit may transition from alower power state to a higher power state and vice versa. In this way,the control circuit may be periodically put to sleep while lockingfunctionality remains active. The duration of the sleep state isindicated at 606 and the duration of the activated state is indicated at608. To allow the control circuitry to be put to sleep while lockingfunctionality remains active, the sleep duration 606 may be less thanthe time scale of the locking operation. For example, the sleep duration606 may be 60-80 ms and the time scale of locking operation may be onesecond, in one use-case scenario. In this way, the control circuit maybe periodically put in a lower power state to reduce the heat generatedby the circuit while locking remains operational.

In the plots illustrated in FIG. 6 , the sleep and activation durationsremain substantially unchanged. However, in other embodiments, thelengths of the durations of the circuit's activation and sleep statesmay be dynamically adjusted based on or more operating conditions, suchas circuit temperature, ambient temperature, the circuit's programmaticcontrol strategy, and the like. For example, responsive to an increasein circuit temperature, the duration of the sleep state may beincreased, to reduce the circuit's temperature and the likelihood of acircuit over-temperature condition. In other examples, the duration ofthe sleep state may be decreased responsive to a decrease in circuittemperature and/or ambient temperature. In this way, the length of thesleep duration may be dynamically increased and/or deceased based onchanges in the differential system, vehicle, and/or operatingenvironment.

The systems and methods described herein have the technical effect ofincreasing the circuit board assembly's packaging efficiency as well asincreasing the circuit board's longevity through a reduction in thecircuit's operating temperature. The systems and methods describedherein may further have the technical effect of increasing the precisionof differential locker control.

FIGS. 1-4 show example configurations with relative positioning of thevarious components. If shown directly contacting each other, or directlycoupled, then such elements may be referred to as directly contacting ordirectly coupled, respectively, at least in one example. Similarly,elements shown contiguous or adjacent to one another may be contiguousor adjacent to each other, respectively, at least in one example. As anexample, components laying in face-sharing contact with each other maybe referred to as in face-sharing contact. As another example, elementspositioned apart from each other with only a space there-between and noother components may be referred to as such, in at least one example. Asyet another example, elements shown above/below one another, at oppositesides to one another, or to the left/right of one another may bereferred to as such, relative to one another. Further, as shown in thefigures, a topmost element or point of element may be referred to as a“top” of the component and a bottommost element or point of the elementmay be referred to as a “bottom” of the component, in at least oneexample. As used herein, top/bottom, upper/lower, above/below, may berelative to a vertical axis of the figures and used to describepositioning of elements of the figures relative to one another. As such,elements shown above other elements are positioned vertically above theother elements, in one example. As yet another example, shapes of theelements depicted within the figures may be referred to as having thoseshapes (e.g., such as being circular, straight, planar, curved, rounded,chamfered, angled, or the like). Additionally, elements coaxial with oneanother may be referred to as such, in one example. Further, elementsshown intersecting one another may be referred to as intersectingelements or intersecting one another, in at least one example. Furtherstill, an element shown within another element or shown outside ofanother element may be referred as such, in one example. In otherexamples, elements offset from one another may be referred to as such.Elements having a continuous shape may be referred to as such, in onexample. Further in another example, elements having a monolithic shapemay be referred to as such. As used herein, the terms “substantially”and “approximately” are construed to mean plus or minus five percent orless of the range or value unless otherwise specified.

The invention will be further described in the following paragraphs. Inone aspect, a differential system is provided that comprises anelectromagnetic solenoid actuator including a coil assembly and a pistonand configured to selectively induce locking and unlocking of axle shaftspeed differentiation; and a circuit board assembly configured toprogrammatically control the electromagnetic solenoid actuator andincluding control circuitry and a sensor that is configured to sense aposition of the piston and radially extends down a face of the coilassembly; wherein the sensor and the control circuitry are enclosed in asealed housing.

In another aspect, a method for operation of a differential system isprovided that comprises at a circuit board assembly that is directlycoupled to a coil assembly in an electromagnetic solenoid actuator,selectively locking and unlocking speed differentiation between a pairof axle shafts based on signals from a sensor included in the circuitboard assembly; and periodically placing control circuitry in thecircuit board assembly in a lower power consuming state for a selectedduration. In one example, the method may further comprise adjusting alength of the selected duration based one or more operating conditions.In a further example, the method may additionally comprise sending acircuit board state update to a vehicle ECU via a CAN or a LIN. Inanother example, the method may further comprise implementing at leastone of a sensor diagnostic routine and electromagnetic solenoid actuatordiagnostic routine to determine if the sensor and/or the electromagneticsolenoid actuator has been degraded.

In yet another aspect, a locking differential system is provided thatcomprises an electromagnetic solenoid actuator including a coil assemblyand a piston and configured to selectively induce locking and unlockingof axle shaft speed differentiation; and a circuit board assemblyconfigured to programmatically control the electromagnetic solenoidactuator and including control circuitry and a sensor that is configuredto sense a position of the piston and extends down a face of the coilassembly from a housing section that includes a planar surface; whereinthe sensor and the control circuitry are enclosed in a continuoushousing; and wherein the circuit board assembly includes executableinstructions stored in non-transitory memory that cause the circuitboard assembly to periodically transition the circuit board assemblybetween an activated state and a sleep state.

In any of the aspects or combinations of the aspects, the circuit boardassembly may include executable instructions stored in non-transitorymemory that cause the circuit board assembly to: periodically place thecircuit board assembly in a lower power consuming state for a selectedduration.

In any of the aspects or combinations of the aspects, the circuit boardassembly may include executable instructions stored in thenon-transitory memory that cause the circuit board assembly to send acircuit board state update to a vehicle controller.

In any of the aspects or combinations of the aspects, the circuit boardassembly may include executable instructions stored in thenon-transitory memory that cause the circuit board assembly to adjustthe selected duration based on one or more operating conditions.

In any of the aspects or combinations of the aspects, the circuit boardassembly may be periodically placed in the lower power consuming statewhile the electromagnetic solenoid actuator is in a lockedconfiguration.

In any of the aspects or combinations of the aspects, the sensor may bearranged perpendicular to the control circuitry.

In any of the aspects or combinations of the aspects, the circuit boardassembly may include a continuous base that comprises an upper sectionand a side section that radially extends towards a central axis of thedifferential system from the upper section.

In any of the aspects or combinations of the aspects, the sensor and theface of the coil assembly may be parallel to one another.

In any of the aspects or combinations of the aspects, theelectromagnetic solenoid actuator may further comprise a housing atleast partially circumferentially enclosing the coil assembly and thepiston; wherein the housing may include a cut-out that mates with andseals at least a portion of the sealed housing.

In any of the aspects or combinations of the aspects, the circuit boardassembly may include a LIN wiring harness.

In any of the aspects or combinations of the aspects, the controlcircuitry may be spaced away from an outer circumferential surface ofthe coil assembly and the sealed housing may include a circuit boardcover that extends laterally away from the sensor.

In any of the aspects or combinations of the aspects, the controlcircuitry may be arranged on an upper side of the electromagneticsolenoid actuator spaced away from a lubricant reservoir.

In any of the aspects or combinations of the aspects, the circuit boardstate update may be sent to the vehicle controller during operation ofthe circuit board assembly in an activated state.

In any of the aspects or combinations of the aspects, selectivelylocking speed differentiation between the pair of axle shafts mayinclude, in a first stage, energizing the coil assembly with a highercurrent and, in a second stage, energizing the coil assembly with alower current.

In any of the aspects or combinations of the aspects, the circuit boardassembly may include a wiring harness with a plurality of wire portsthat are arranged along an axis parallel to a central axis of thelocking differential system.

In another representation, a differential locker is provided whichcomprises an electromagnetic solenoid configured to actuate a lockinggear and collocated with sensing, control, and diagnostic circuitry thatis sealed in a monolithic housing coupled to a face on an interior axialside of the electromagnetic solenoid, wherein the sensing, control, anddiagnostic circuity is configured to initiate locking and unlocking ofthe locking gear and determine a position of the electromagneticsolenoid.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example, and notlimitation. It will be apparent to persons skilled in the relevant artsthat the disclosed subject matter may be embodied in other specificforms without departing from the spirit of the subject matter. Theembodiments described above are therefore to be considered in allrespects as illustrative, not restrictive.

Note that the example control and estimation routines included hereincan be used with various vehicle system configurations. The controlmethods and routines disclosed herein may be stored as executableinstructions in non-transitory memory and may be carried out by thecontrol system including the controller in combination with the varioussensors, actuators, and other system hardware. The specific routinesdescribed herein may represent one or more of any number of processingstrategies. As such, various commands, operations, and/or actionsdescribed herein may be performed in the sequence illustrated, intandem, or in some cases omitted. Likewise, the order of processing isprovided for ease of description and is not necessarily required toachieve the features and advantages of the examples described herein.One or more of the actions, operations, and/or functions, describedherein may be repeatedly performed depending on the particular strategybeing used. Further, the described actions, operations, and/or functionsmay graphically represent code to be programmed into non-transitorymemory of the computer readable storage medium in a differential controlsystem, where the described actions are carried out by executing theinstructions in a system including the various hardware components incombination with the electronic controller.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific examples are notto be considered in a limiting sense, because numerous variations arepossible. For example, the above technology may be applied to motorsystems with different configurations and in a vehicle with a variety ofpropulsion sources such as motors, engines, combinations thereof, etc.Moreover, the terms “first,” “second,” “third,” and the like are notintended to denote any order, position, quantity, or importance, butrather are used merely as labels to distinguish one element fromanother, unless explicitly stated to the contrary. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother functions, features, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither excluding nor requiring two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether narrower, broader,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. A method for operation of a differentialsystem, comprising: at a circuit board assembly that is directly coupledto a coil assembly in an electromagnetic solenoid actuator, selectivelylocking and unlocking speed differentiation between a pair of axleshafts based on signals from a sensor included in the circuit boardassembly; and periodically placing control circuitry in the circuitboard assembly in a lower power consuming state for a duration which isless than a duration of locking or unlocking speed differentiation. 2.The method of claim 1, further comprising adjusting a length of theduration of the lower power consuming state based one or more operatingconditions.
 3. The method of claim 1, further comprising sending acircuit board state update to a vehicle controller via a controller areanetwork (CAN) or a local interconnect network (LIN).
 4. The method ofclaim 3, wherein the circuit board state update is sent to the vehiclecontroller during operation of the circuit board assembly in anactivated state.
 5. The method of claim 1, wherein selectively lockingspeed differentiation between the pair of axle shafts includes, in afirst stage, energizing the coil assembly with a higher current and, ina second stage, energizing the coil assembly with a lower current. 6.The method of claim 1, further comprising implementing at least one of asensor diagnostic routine and electromagnetic solenoid actuatordiagnostic routine to determine if the sensor and/or the electromagneticsolenoid actuator has been degraded.
 7. The method of claim 1, whereinthe control circuitry is repeatedly cycled between the lower powerconsuming state and a higher power consuming state.
 8. The method ofclaim 1, wherein periodically placing the control circuitry in the lowerpower consuming state comprises cycling between the lower powerconsuming state and a higher power consuming state.
 9. The method ofclaim 1, wherein the duration of the lower power consuming state is lessthan half a second.
 10. The method of claim 9, wherein, in the lowerpower consuming state, a state of the control circuitry is stored inmemory and the remaining systems of the control circuitry are placed ina minimum power consuming state.
 11. A method for operation of adifferential system, comprising: providing a circuit board assembly thatis directly coupled to a coil assembly in an electromagnetic solenoidactuator, the circuit board assembly enclosed and sealed in a firsthousing that mates with a cut-out of a second housing that encloses thecoil assembly and a piston of the actuator, the cut-out sealing at leasta portion of the first housing; selectively locking and unlocking speeddifferentiation between a pair of axle shafts based on signals from asensor included in the circuit board assembly; and periodically placingcontrol circuitry in the circuit board assembly in a lower powerconsuming state for a selected duration.
 12. The method of claim 11,further comprising adjusting a length of the selected duration based oneor more operating conditions, including a temperature.
 13. The method ofclaim 11, wherein selectively locking speed differentiation between thepair of axle shafts includes, in a first stage, energizing the coilassembly with a higher current and, in a second stage, energizing thecoil assembly with a lower current.
 14. The method of claim 11, whereinthe control circuitry is repeatedly cycled between the lower powerconsuming state and a higher power consuming state.
 15. The method ofclaim 11, wherein periodically placing the control circuitry in thelower power consuming state comprises cycling between the lower powerconsuming state and a higher power consuming state, and wherein aduration of the lower power consuming state is less than a duration oflocking or unlocking speed differentiation.
 16. The method of claim 11,wherein the duration of the lower power consuming state is less thanhalf a second.
 17. The method of claim 11, wherein, in the lower powerconsuming state, a state of the control circuitry is stored in memoryand systems of the control circuitry other than the memory are placed ina minimum power consuming state.